Mobile wireless communications systems, such as GSM/GPRS (Global System Mobile/General Radio Packet Service) systems, include base stations that can communicate with large numbers of mobile stations. The base stations periodically transmit a reference signal known as a frequency burst (FB) on a broadcast control channel (BCCH) to enable the mobile stations to synchronize with the base stations. The purposes of the frequency burst are twofold, namely frequency calibration and coarse timing. First, with respect to frequency calibration of the mobile station, the frequency burst enables correction of the frequency offset or error between the local carrier frequency of the mobile station and the carrier frequency of the base station. Second, with respect to coarse timing, approximate time alignment with the beginning of the frequency burst is performed so that a fine tuning can be conducted in the later acquisition of a sync burst (SB) from the base station.
These mobile communication systems typically include radio frequency front ends with analog circuitry that is very noise and interference sensitive. In some applications, the RF circuitry may need to detect signals as small as a few micro-volts in amplitude. If this RF circuitry encounters noise, it is possible that receive performance will be substantially degraded. These systems often employ signal processing circuitry such as a digital signal processor (DSP) to search for the frequency burst (FB) signal and a microcontroller unit (MCU) to govern the overall operation of the system. The digital circuitry of the DSP and MCU produces digital signals with relatively small rise and fall times, or with fast transitions or sharp edges. The large size and the high gate count of the DSP and MCU are factors which contribute to the substantial amount of noise that may be produced in the vicinity of the DSP and MCU. Unfortunately, it is possible that this digitally generated noise may significantly interfere with the operation of radio frequency circuitry of the system.
What is needed is an apparatus and methodology which achieves frequency burst acquisition without subjecting radio frequency circuitry to substantial amounts of noise.